Study on mechanical properties and damage evolution of carbonaceous shale under triaxial compression with acoustic emission

Abstract

To explore the mechanical properties and damage evolution characteristics of carbonaceous shale with different confining pressures and water-bearing conditions, triaxial compression tests accompanied by simultaneous acoustic emission (AE) monitoring were conducted on carbonaceous shale rock specimens. The AE characteristics of carbonaceous shale were investigated, a damage assessment method based on Shannon entropy of AE was further proposed. The results suggest that the mechanical properties of carbonaceous shale intensify with increasing confining pressure and degrade with increasing water content. Moisture in rocks does not only weaken the cohesion but also reduce the internal friction angle of carbonaceous shale. It is observed that AE activities mainly occur in the post-peak stage and the strong AE activities of saturated carbonaceous shale specimens appear at a lower normalized stress level than that of natural-state specimens. The maximum AE counts and AE energy increase with water content while decrease with confining pressure. Both confining pressure and water content induce changes in the proportions of AE dominant frequency bands, but the changes caused by confining pressure are more significant than those caused by water content. The results also indicate that AE entropy can serve as an applicable index for rock damage assessment. The damage evolution process of carbonaceous shale can be divided into two main stages, including the stable damage development stage and the damage acceleration stage. The damage variable increases slowly accompanied by a few AE activities at the first stage, which is followed by a rapid growth along with intense acoustic emission activities at the damage acceleration stage. Moreover, there is a sharp rise in the damage evolution curve for the natural-state specimen at the damage acceleration stage, while the damage variable develops slowly for the saturated-state specimen.

Crack propagation characteristics during progressive failure of circular tunnels and the early warning thereof based on multi-sensor data fusion

“…Before rock failure, there are abnormal responses in multiple physical fields: these include abrupt increases of deformation and displacement (Xu et al 2020;Wang et al 2021a, b), occurrence of an AE quiet period (Chmel et al 2013;Luo et al 2022), a steep drop in the AE-based b value (Triantis et al 2018;Selahattin et al 2018), abrupt increases of AE entropy (Zhang et al 2015;Yang et al 2021) and covariance of the strain field (Zhang et al 2021a, b;Zhang et al 2020), occurrence of a high-temperature zone under thermal infrared radiation (Tang et al 2010;Ma et al 2013), and the abrupt increment of electromagnetic radiation frequency (Xu et al 2016). Previous research found that the responses and failure precursors of tunnels are not synchronous across physical fields (Zhou et al 2020;Li et al 2021).…”

Damage mechanism characterization of ±35° and ±55° FW composite tubes using acoustic emission method

“…To calculate the energy of AE signals for each frequency interval, the Packed Wavelet Transform (WPT) was utilized. The analysis of each of these components was performed by applying the power spectrum analysis using Fast Fourier Transform (FFT) (Ni and Iwamoto, 2002;Oskouei et al, 2009;Wojtaszczyk, 1997;Xu et al, 2020;Yang et al, 2021). In this regard, the discrete wavelet transform (WT) is one of the most widely used types of wavelet transforms, in which the main signal is decomposed into some components called generalities and details.…”

“…(2004) investigated the influence of winding angles and various fiber on the mechanical properties and failure mechanisms of FW composite tubes. Several studies on the effect of material and manufacturing parameters such as fibers orientation (Özbek and Bozkurt, 2019a), intraply fiber hybridization (Özbek et al., 2019b), and stacking sequence (Gemi et al., 2020a, 2020b; Yazman, 2021) on the crashworthiness behavior of the FW composite pipes have been published. In other studies, (Almeida Jr et al., 2019; Deniz et al., 2013; Gemi et al., 2009; Karami et al., 2015; Kordkheili et al., 2021), researchers investigated the effects of various parameters on the mechanical behavior of FW composite structures through experimental and numerical analysis.…”

A new statistical damage model for true triaxial pre-and post-peak behaviors of rock considering intermediate principal stress and initial compaction effects

“…To study the mechanical properties of rocks, a large number of uniaxial compression tests and conventional triaxial compression tests (CTC: σ 1 > σ 2 = σ 3 ) have been carried out, and rich research results have been obtained (Wang et al., 2021, 2022a; 2022b; Xiao et al., 2020; Yang et al., 2008, 2021; Zhao et al., 2013; Zhao and Cai, 2010). In terms of strength, the confining pressure effect of rock peak strength is studied, and there are various research results on the effect of σ 3 on residual strength (Hudson et al., 1972).…”